Dimerization of propylene to 2,3-dimethylbutenes

ABSTRACT

Propylene is converted to a mixture of C6 olefins with high efficiency, usually over 70 percent, to 2,3-dimethylbutenes using a highly specific catalyst system and a highly specific solvent at a temperature less than about 10* C. The catalyst system comprises NiCl2, triisopropylphosphine and an aluminum alkyl chloride or dichloride. The solvent is a dichlorinated benzene.

United States Patent Inventors Harold E. Swift Gibsonia; Ching-Youg Wu,O'Hara Township, Allegheny County, both of Pa.

Appl. No. 850,642

Filed Aug. 15, 1969 Patented Nov. 23, 1971 Assignee Gulf Research 8:Development Company Pittsburgh, Pa.

DIMERIZATION OF PROPYLENE TO 2,3-

[56] References Cited UNITED STATES PATENTS 3,467,726 9/1969 Griffin260/683.15 3,482,001 12/1969 Eberhard! 260/683.l5 3,485,892 12/1969Griffin et al. 260168315 3,513,218 5/1970 Faltings et al 260/683.l5

Primary Examiner-Paul M. Coughlan, Jr. Attorneys-Meyer Neishloss, DeaneE. Keith and Richard C.

Gaffney DIMERIZATION OF PROPYLENE TO 2,3- DIMETHYLBUTENES This inventionrelates to a process for the dimerization of propylene in highefficiency to 2,3-dimethylbutenes.

The dimerization of propylene and other olefins by a variety ofcatalysts is well known in the art. Propylene normally dimerizes to formmethylpentenes and n-hexenes, which C olefins are not as valuable as the2,3-dimethylbutenes which can be hydrogenated to form2,3-dimethylbutane, a high octane motor fuel component. It is desirable,therefore, to find a system for directing the dimerization of propyleneto form the more valuable 2,3-dimethylbutenes. Catalyst systems havebeen suggested in the art for the dimerization of propylene and attemptshave been made to selectively direct the reaction to the formation ofthe desired 2,3-dimethylbutenes (see US. Pat. No. 3,390,201). However,the prior art catalyst systems have been relatively weak and require theuse of stabilizers (promoters) or the selectivity to the formation ofthe 2,3- dimethylbutenes, while improved over the use, say, of sulfuricacid, is still too low to 60 percent) to be of real commercial interest.To be commercially attractive the catalyst system must be as simple aspossible while providing for the dimerization of propylene with aselectivity in excess of about 70 percent, preferably in excess of 75percent, to the desired 2,3- dimethylbutenes. A highly specific catalystsystem in combination with a low temperature and a specific solvent hasnow been discovered which overcomes the disadvantages of the prior artsystems and provides a commercially attractive process.

In accordance with the invention, a process has now been discovered forthe selective conversion of propylene to 2,3- dimethylbutenes whichcomprises:

reacting propylene at a temperature less than about 10 .C. in thecontact presence of a liquid dichlorinated benzene solvent and acatalyst complex comprising NiCl triisopropylphosphine and an alkylaluminum chloride having the formula AlR Cl where R is an alkyl grouphaving from one to six carbon atoms and n has a value from one to twoand wherein said complex the mole ratio of phosphorus to nickel is from0.5:1 to 2.521 and the aluminum to nickel mole ratio is from 2:1 to 7:1.

The charge stock olefin is propylene and its source is not critical solong as it is free of contaminants which adversely interact with acatalyst system to be defined below. Substantially pure propylene may beemployed as may a gas containing from 30 to 100 volume percentpropylene, preferably from 50 to 100 volume percent of propylene. Asuitable source of reduced propylene content gases is a refinerypropanepropylene stream obtained from a catalytic cracking unit. Thesestreams normally contain between 60 and 80 volume percent propylene andare suitable for use in the process of this reaction provided they arefree of interfering contaminants such as indicated above. Interferingcontaminants include water, CO sulfur compounds, organic acids or otheroxygen containing materials which are known to interact readily withaluminum alkyls.

The reaction occurs by passing propylene or a propylene containing gasinto liquid dichlorobenzene containing a preformed catalyst complex. Thecatalyst complex consists of three specific components which are admixedin the presence of dichlorobenzene. The three catalyst componentsinclude (1) nickel chloride (NiCl (2) an alkyl aluminum chloride havingthe general formula AIR Cl where R is an alkyl group having from one tosix carbon ibms'afid n has a value from one to two, and (3)triisopropylphosphine. Particularly suitable aluminum componentsinclude, but are not limited to, diethylaluminumchloride,ethylaluminumdichloride and the well-known ethylaluminumsesquichloridewhich is a mixture of diethylaluminumchloride andethylaluminumdichloride, propylaluminumdichloride andhexylaluminumdichloride.

The molar ratio of the catalyst components to each other is important toobtain the best results. For example, the molar ratio of phosphorus tonickel is suitably from 0.5:] to 2.5:],

preferably from 0.75:1 to 1.5:1, and is optionally about 1:]. Similarly,the molar ratio of aluminum to nickel is suitably from 2:1 to 7:1,preferably from 2.5:1 to 65:1, and is optimally from 4: l to 6:1.

The manner of addition of the various catalyst components to each otherto form the desired complex is not critical. Normally, the nickelchloride and phosphine are added to the dichlorobenzene solvent followedby the addition of the aluminum component.

The amount of the catalyst complex dissolved in the reaction system isnot critical and is suitably from 0.05 to 5 weight percent or more basedon the total weight of the catalyst and solvent and is preferably from0.15 to 2.5 weight percent.

The dichlorinated benzene solvent can be any of the liquid dichlorinatedforms or a mixture of one or more of the ortho, meta andparadichlorobenzenes, so long as the mixture is liquid under theconditions of the reaction so it may function as a solvent. The use ofmonochlorinated benzenes gives unsatisfactory selectivities as doalkylated aromatics such as toluene, while the use of mosttrichlorinated benzenes is unsuitable due to their high melting points.Thus, the use of the dichlorinated benzenes is unique, and orthodichlorobenzene is preferred.

It is an important feature of the process of this invention to maintainthe dimerization reaction temperature less than about 10 C. Temperaturestoo far above 10 C., for example, 25 C., result in decreasedefficiencies to the production of the desired 2,3-dimethylbutenes. Thelower temperature limit is the melting point of the reaction system, forthe reaction system must be maintained in the liquid phase. The lowertemperature limit is about 20 C. The preferred reaction temperature arefrom l5 to 5 C. with the optimum temperatures being from l0 to 0 C.

The dimerization reaction conditions, except for temperature, are notcritical. Thus, any suitable pressure can be employed, for example, apressure from 0 to 500 p.s.i.g. or more; however, pressures are usuallyin the range of 0 to p.s.i.g. The reaction time may be quite short forthe reaction is substantially instantaneous and is limited only by masstransfer considerations. Suitable reaction times are as short as 1minute or less but are usually from 30 minutes to 4 hours or more toallow for proper mixing and slow addition of propylene if desired.

The propylene is added to the solution of the catalyst complex in thedichlorinated benzene through a sparger or other device which breaks upthe propylene into small bubbles. Agitation of the contents of thereaction zone is preferred in order to insure better contacting betweenthe propylene and the catalyst.

Reaction may be carried out continuously or batchwise as desired, oreven in a coil-type reactor.

The invention will be further described with reference to the followingexperimental work. In all of the experiments to follow, either the CPgrade propylene or the propylenepropane refinery stream were passedthrough a column of molecular sieves to reduce their moisture content.All solvents were distilled, stored under a nitrogen atmosphere, anddried with molecular sieves. The organoaluminum compounds and phosphineswere, of course, stored under a nitrogen atmosphere at all times. Thenickel chloride employed was also, of course, anhydrous.

The procedure for a typical propylene dimerization experiment was asfollows. Into a 300 milliliter thick wall glass reactor with a 200p.s.i.g. safety pressure release disc was added 1.5 millimoles ofanhydrous nickel chloride and 1.5 millimoles of triisopropylphosphine in50 milliliters of orthodichlorobenzene. This was followed by addition ofa solution of 3.7 millimoles of ethylaluminumsequichloride in 50milliliters of orthodichlorobenzene. The reactor was then sealed and themixture agitated with a magnetic stirrer. The reactor was then cooled to-10 C. and propylene was introduced at the rate of 0.56 liters perminute for 20 minutes to give 0.5 moles of propylene in the reactor. Thetemperature was maintained at --l:5 C. The maximum pressure during thecharge of propylene was 4 p.s.i.g. and it dropped to 0 in less than 30minutes. After an additional hour of stirring at -l00 C. the temperaturewas brought to room temperature. No unreacted propylene was recovered.

Two separate gas liquid chromatographic analyses were made to determineconversion and selectivity values. To obtain data for the determinationof conversion, a -foot column /4-inch O.D. packed with 10 percentCarbowax on chromosorb W was temperature programmed linearly at a rateof 10 per minute. For selectively determination, a 50-foot column85-inch O.D. packed with 30 percent adiponitrile on chromosorb P wasused isothermally at 50 C. Using the second column, separate gas liquidchromatographic peaks were obtained for cis-4-methyl-2-pentene,2,3-dimethyl-l-butene; trans-3-hexene; 2-methyl-2-pentene; cis-Z-hexeneand 2,3-dimethyl-2-butene, but unresolved peaks were obtained for amixture of 4-methyl-l-pentene, and trans-4-methyl-2- pentene and for amixture of 2-methyl-lpentene and trans-2- hexene.

A first series of runs was made to show the effect of various phosphineligands and solvents on the selectivity of the system for the productionof the desired 2,3-dimethylbutenes. In all of these runs the systemconsisted of 1.5 millimoles of nickel chloride (NiCl,); l.5 millimolesof the phosphine; 3.7 millimoles of ethylaluminumsesquichloride; 100milliliters of solvent and 0.5 moles of propylene. The reaction was runin most cases at TABLE I.EFFECT OF PHOSPHINE LIGAND A second series ofruns were made showing the effect of temperature and solvent on theselectivity to produce 2,3- dimethylbutenes using a catalyst systemcomposed of 1.5 millimoles of M031 3.7 millimoles of aluminumsesquichloride and L5 millimoles of triisopropylphospine. The resultsare shown in table ll below.

Referring to table ll, it can be seen that temperatures from -l0 to 25C. have little, if any, effect on the selectivity of the process for theproduction of 2,3-dimethylbutenes when toluene or chlorobenzene are usedas the solvents (examples l0 and ll). Quite unexpectedly, temperaturehas a telling effect on the yield of 2,3-dimethylbutenes when 0-dichlorobenzene is used as the solvent (example l2).'At

25 C., the effect of o-dichlorobenzene is about the same aschlorobenzene, which is similar to the effect of toluene. At 0 C., thepercent selectivity to 2,3-dimethylbutenes jumps from 55 percent to over70 percent when o-dichlorobenzene is used l0 C. for 2 hours atatmospheric pressure. The results of the runs are shown in table 1above.

Referring to table l, it can be seen that triisopropylphosphine inorthodichlorobenzene gave the highest conversion with the highestselectively to 2,3-dimethylbutenes. The selectivity dropped dramaticallywhen tri-n-butylphosphine or triphenylphosphine were employed inorthodichlorobenzene (examples 3 and 4). Results in examples 5-9 showthat both the conversion and the selectivity to the production of 2,3-dimethylbutenes suffered when toluene or chlorobenzene were employed inplace of orthodichlorobenzene as the solvent. For example, even withtriisopropylphosphine the selectivity in toluene was reduced from 81percent (example 1) to 49 percent (example 5) and the conversion from 95percent to 82 percent.

Thus, the data in table I shows that in order to obtain the highconversions and high selectivities (above 75 percent) to as the solvent(example l2). This was totally unexpected in view of the data obtainedusing toluene or chlorobenzene (examples l0 and l 1). Furtherimprovements in selectivity were obtained by operating atl0.C. as shownin example 12.

50 sieves. The gas mixture was introduced at I00 p.s.i.g. head pressureto prevent condensation of propane in the gas line The results of thisseries of experiments are shown in table Ill below.

Referring to table Ill below, example l3 using an untreatedpropane-propylene refinery stream resulted in poor conversions andselectivities to the formation of the desired 1,2- dimethylbutenes.Pretreatment of the refinery propanepropylene stream with molecularsieves to reduce the water and sulfur content resulted, as shown inexample 14, in excellent conversions and improved selectivities. The useof a synthetic mixture of 68 mole percent pure propylene and 32 TABLEIIL-DIMERIZATION WITH PROPYLENE-PROPANE MIXTURE I Contains about 200ppm. of H10 and about 8 p.p.m. of sulfur 1 Pretreated wlth mo ocularsieves to reduce H 0 and sulfur.

i Pure proqylene mixed with pure grade propane.

mole percent pure propane resulted in greatly improved selectivities andconversions over the untreated refinery stream as shown by a comparisonof examples 13 and 15.

having the formula AIR,.Cl =,l where R is an alkyl group having from oneto six carbon atoms and n has a value from 1 to 2 and wherein saidcomplex the mole ratio of phosphorus to nickel is about 1:1 and thealuminum to nickel mole ratio is from 2:1 to 7:1.

2. A process according to claim 1 wherein the alkyl group in the alkylaluminum chloride catalyst component is ethyl.

3. A process according to claim 2 wherein the reaction temrst mrsiifr w11 C- In all of the tables of data, the conversion figures are in molepercent and indicate the mole percent of the propylene in the chargestock which has been converted. The selectivity figures in all of thetables are also in mole percent and indicate the mole percent of thepropylene converted which is present in the product as the desired2,3-dimethylbutenes.

Resort may be had to such variations and modifications astriisopropylphosphine and an alkyl alumirTum chlEoi'E 4. A processaccording to claim 3 wherein the molar ratio of aluminum to nickel isfrom 2.5:1 to 65:1.

5. A process according to claim 1 plus recovering a reaction productcomprising at least 70 percent by weight of dimethylbutenes 6. A processfor the selective dimerization of propylene in a propylene containinggas to a mixture of 2,3-dimethyldimethylbutenes -butene and2,3-dimethyl-2-butene which comprises contacting said propylenecontaining gas with a catalyst complex dissolved in ortho-dichlorobenzene as a solvent under dimen'zation conditions, including atemperature below about 10' C., said catalyst complex comprising NiCl,,triisopropylphosphine and an alkyl aluminum chloride having the formulaAlRnCl3=,. where R is an alkyl group having from one to six carbon atomsand n has a value from 1 to 2 and wherein said complex the mole ratio ofphosphorus to nickel is about 1:1 and the aluminum to nickel mole ratiois from 2:1 to

7. A process according to claim 6 wherein the propylene containing gasis substantially pure propylene.

8. A process according to claim 6 wherein the propylene containing gasis a refinery propane-propylene stream containing from 50 to volumepercent propylene.

9. A process according to claim 7 wherein the aluminum alkyl chloride isethyl aluminumsesquichloride.

* II! t t t mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3 ,522 Dated November 23, 1971 I m Harold E. Swift andChing-Yong Wu It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

j Col. 1, lines 39 and 65; Col. 5, line 4; and Col. 6, line 15,

" AIR Cl should be AlR Cl Col. 2 line 70, "ethylaluminumsequichloride"should be ethylaluminumsesquichloride Col. 3, line 4, "lOOC. should belOC.

Col. 4, Table II, the Example No. "11" should be inserted over the"Chlorobenzene column.

Col. 6, lines 8 and 9, "2 ,3dimethyl-dimethylbutenes-butene" should read2,3-dimethyl-l-butene Col. 5, lines 4 through 27, and Col. 6, line 1should be rearranged to read as follows:

In all of the tables of data, the conversion figures are in the molepercent and indicate the mole percent of the propylene in the chargestock which has been converted. The selectivity figures in all of thetables are also in mole percent and indicate the mole percent of thepropylene converted which is present in the product as the desired2,3-dimethylbutenes.

Resort may be had to such variations and modifications as fall withinthe spirit of the invention and the scope of the appended claims.

We claim:

1. A process for the selective conversion of propylene todimethylbutenes which comprises:

[Continued on page 2] UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent N 3,622 ,649 Dated November 23, 1971 Inventofls)Harold E. Swift and Ching-Yong Wu It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

[- [Page 2] reacting propylene at a temperature less than about 10C, inthe contact presence of orthodichloro benzene as a solvent and acatalyst complex comprising NiCl triisopropylphosphine and an alkylaluminum chloride having the formula AlR Cl where R is an alkyl grouphaving from one to six carbon atoms and n has a value from 1 to 2 andwherein said complex the mole ratio of phosphorus to nickel is about 1:1 and the aluminum to nickel mole ratio is from 2 :l to 7 :l.

2. A process according to claim 1 wherein the alkyl group in the alkylaluminum chloride catalyst component is ethyl.

3. A process according to claim 2 wherein the reaction temperature isfrom l5C. to 5C.

Signed and sealed this LLth day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GUTTSCHALK Attesting Officer Commissionerof Patents

2. A process according to claim 1 wherein the alkyl group in the alkylaluminum chloride catalyst component is ethyl.
 3. A process according toclaim 2 wherein the reaction temperature is from -15* C. to 5* C.
 4. Aprocess according to claim 3 wherein the molar ratio of aluminum tonickel is from 2.5:1 to 6.5:1.
 5. A process according to claim 1 plusrecovering a reaction product comprising at least 70 percent by weightof dimethylbutenes
 6. A process for the selective dimerization ofpropylene in a propylene containing gas to a mixture of2,3-dimethyl-dimethylbutenes -butene and 2,3-dimethyl-2-butene whichcomprises contacting said propylene containing gas with a catalystcomplex dissolved in ortho-dichloro benzene as a solvent underdimerization conditions, including a temperature below about 10* C.,said catalyst complex comprising NiCl2, triisopropylphosphine and analkyl aluminum chloride having the formula AlRnCl3 n where R is an alkylgroup having from one to six carbon atoms and n has a value from 1 to 2and wherein said complex the mole ratio of phosphorus to nickel is about1:1 and the aluminum to nickel mole ratio is from 2:1 to 7:1.
 7. Aprocess according to claim 6 wherein the propylene containing gas issubstantially pure propylene.
 8. A process according to claim 6 whereinthe propylene containing gas is a refinery propane-propylene streamcontaining from 50 to 100 volume percent propylene.
 9. A processaccording to claim 7 wherein the aluminum alkyl chloride is ethylaluminumsesquichloride.